In a scenario in which a direct current source is applied, an output voltage of the direct current source should be limited to a safe range in a process of performing maintenance or dealing with other emergencies. A protection device as shown in FIG. 1 may be adopted. Specifically, an electronic switch S1 may be switched on, so that an output terminal of a direct current source is short-circuited and an output voltage of the direct current source is limited to the safe range.
The failure mode of the electronic switch S1 is generally a mode in which the electronic switch S1 is short-circuited, and the protection will be provided even if the electronic switch S1 is in the failure mode. However, it is difficult for the device for protecting the direct current source in the short-circuited mode to provide a driving voltage for the electronic switch S1, since there is no sufficient drive voltage to drive the electronic switch S1 to be switched on in the absence of an additional power supply in a case that the direct current source is short-circuited. As shown in FIG. 1, if the driving voltage of the electronic switch S1 is provided by the direct current source, the output voltage of the direct current source will be maintained in a minimum required voltage for driving the electronic switch S1. Therefore, the electronic switch S1 has a relatively large conduction loss and even cannot work for a long time.